Investigation of the Hydrolytic Stability of the HLDF-6-AA Antitumor Peptide by the Method of Accelerated Aging

The HLDF-6 hexapeptide corresponded to the 41–46 (TGENHR) fragment of the Human Leukemia Differentiation Factor (HLDF) and exhibited a wide spectrum of neuroprotective, normalizing, anxiolytic, nootropic, and antitumor activity. Its N-acetyl C-amide form (Ac-TGENHR-NH2, HLDF-6-AA) was prepared by the solid phase peptide synthesis and served as a basis for a creation of a promising antitumor drug. The hydrolytic stability of this pharmaceutical dosage form of the HLDF-6-AA peptide was studied by the method for an accelerated aging in aqueous solutions at 60°С. The structures of the peptide which were formed after a hydrolysis were analyzed by HPLC and mass spectrometry. The pharmaceutical dosage form of the HLDF-6-AA peptide was found to be practically completely hydrolyzed in solution at 60°С within 30 days. The Asn residue in the Ac-TGENHR-NH2 peptide was hydrolyzed to the Asp residue with the formation of the Ac-TGEDHR-NH2 and Ac-TGED(HR-NH2)-ОН peptides which had α and β bonds between Asp and His, respectively. We concluded on the basis of the results of the accelerated aging that a storage of the peptide dosage form as aqueous solutions did not provide the stability necessary for a pharmaceutical drug. The required stability of the dosage form was achieved during the storage of the HLDF-6-AA peptide as a powder that was lyophilized under sterile conditions.